Atherosclerosis is a major medical problem responsible for a degree of morbidity and mortality as a result of limb ischemia, stroke and myocardial infarction. Current revascularization therapies to relieve the condition include arterial bypass surgery, percutaneous transluminal angioplasty and thrombolysis of clot.
There are numerous disadvantages associated with these current methods for vascular reperfusion of an ischemic area. Cardiac artery bypass surgery and bypass surgery for ischemic limbs entails extensive and complicated surgery, and requires that the patient have adequate lung function and kidney function in order to tolerate the circulatory bypass necessary for the procedure. The complications associated with this surgery are directly related to the time that the patient is on circulatory bypass. These complications include strokes, renal failure, and ultimately the inability to resuscitate the heart. Other immediate complications of such surgery include strokes and heart attacks during or as a consequence of the surgery. Some patients are not relieved of their anginal symptoms after the bypass surgery, and some develop a graft closure immediately or within the first year following the procedure. Bypass grafting for ischemic limbs and threatened strokes entails prolonged and extensive surgery and is also greatly limited by the above-described complications.
More recently the development of balloon angioplasty utilizing a catheter device that can cross an obstructive intravascular lesion has permitted a less invasive approach with good results in a small percentage of patients without the necessity for the risk of major surgery. With this technique a balloon carried on the catheter is threaded across an obstruction of plaque and inflated to destroy the plaque. This technique, however, requires the ability to cross the obstruction with the catheter. Hard obstructions may be impossible to cross and are not generally successfully removed or destroyed by this technique. Moreover, because of the size of the catheter and balloon involved, the vessels that can be entered are limited to the larger or moderately large size vessels.
Laser radiation shares properties with regular light; however, its monochromaticity and coherence give it special characteristics. The property of monochromaticity of the laser allows differential absorption of various wavelengths by specific tissues. The coherence and high amplification of laser energy is a quality which makes the laser useful as a cutting or burning instrument. The cardiovascular applications for laser radiation have not been investigated until recently. Little is known about the long-term photobiological effects of laser radiation on vascular tissues and cells. However, because of its light properties, the laser beam is capable of delivery through flexible optical fibers made of silica or quartz which can be passed through vascular catheters and is, therefore, capable of being localized at various sites within the arteries and veins. This particular quality of laser energy, in addition to its ability to photocoagulate and cut tissues, makes it a potentially suitable instrument to open or widen obstructive lesions within the vascular system. There are, however, a number of problems with the intravascular use of laser radiation for the treatment of cardiovascular conditions, and these have, in the past, limited such use in humans.
A major recurring problem which has been encountered with the intravascular delivery of laser energy using optical fibers is vascular perforation. The manipulation of optical fibers inside arteries is difficult, and inadequate steerabilty and positioning of the fiber can result in mechanical perforation of the vessel wall as at curves or branches. Vascular perforation may also result from thermal damage to the vessel wall, as, for example, because of dispersion of the laser beam beyond the plaque or improper positioning of the optical fiber so that it directs laser energy directly into the vessel wall. The risk of mechanical perforation may be minimized by putting the optical fiber into a catheter system which has a steerable guide wire similar to that currently used for balloon angioplasty. Preventing thermal perforation of the vessel has been more difficult to achieve.
One known system attempts to avoid thermal perforation by employing the laser radiation solely for heating a metal tip on the end of the fiber and using the heated tip to burn through the plaque. While this technique may avoid perforation due to the laser beam impinging directly onto the vessel wall, it does not prevent thermal perforation. The tip itself may burn through the wall. Moreover, tissue, as of the vessel wall, may stick to the hot tip, causing the tissue to tear as the tip is moved and producing a thrombosis. This technique also requires mechanical pressure to force the tip through the plaque, and has not been very successful with blockages located at any substantial distance from the entry point of the catheter, or in small winding cardiac arteries, since sufficient mechanical pressure cannot be exerted on the tip to force it through the plaque.
Moreover, methods and systems proposed to date for the utilization of lasers to remove plaque from blood vessels require the exclusion of blood from the vessel in the area of the plaque and the necessity for providing means for removing debris from the vessel, such as by suction device, etc. Also, the destruction of a hard to remove material such as plaque without concomitant damage to the surrounding vessel walls has been difficult to achieve.
The properties of laser radiation offer the potential of its use for treating other cardiac conditions, such as for destroying abnormal conduction tissue in the heart, e.g., the bundle of His, or for the occlusion of undesirable vascular channels. There has, however, been no reported success in the utilization of laser systems for such purposes.
It is an object of the present invention to provide a method particularly adapted for the efficacious and safe recanalization of blood vessels obstructed by plaque with a laser which is not subject to the disadvantages discussed heretofore.
It is a further object of the invention to provide a method for the occlusion of undesirable cardiovascular channels employing a laser.
It is still a further object of the invention to provide a method for the revascularization of cardiovascular tissue employing a laser based system.
It is still a further object of the invention to provide a method for the location and destruction of conduction tissue in the heart utilizing a laser based system.